A power combiner can be used to combine the power of two signals, i.e. to add the signals. A power splitter can be used to split the power into two signals, for example two substantially identical signals each comprising a substantially equal portion of the power of the input signal. Some power combiners can also be used as power splitters depending on how they are connected to input signals.
One example of a power splitter and combiner is a Wilkinson power combiner. One advantage of a Wilkinson power combiner is isolation of two input signals, so that one input signal does not appear at the other input terminal, which could cause distortion in a driving circuit.
FIG. 1 shows an example of a Wilkinson power combiner 100, when used as a power combiner. The power combiner 100 includes a curved conductor or transmission line 102. A first input signal is provided to one end 104 of the transmission line 102, and a second input signal is provided to the other end 106. An output signal is taken from a mid point 108 of the transmission line 102. A resistor 110 is connected between the ends 104 and 106 of the transmission line 102.
The power combiner 100 is arranged such that a propagation delay or phase shift of an input signal between either end 104 and 106 and the mid point 108 is λ/4, where λ is preferably substantially the wavelength of at least one of the input signals. Thus a path from input 104 to mid point 108 is a quarter-wave transmission line, as is a path from input 106 to mid point 108. A characteristic impedance between either end 104 and 106 and the mid point 108 is √{square root over (2)}Z0. The resistance of the resistor 110 is 2Z0.
In use, when input signals are applied to the ends 104 and 106, a mixed signal is obtained at mid point 108.
Kim et al. (2012), “A Fully-Integrated High-Power Linear CMOS Power Amplifier With a Parallel-Series Combining Transformer,” IEEE Journal of Solid-State Circuits, Volume 47, Issue 3, March 2012, 599-614 describes a linear CMOS power amplifier for high data-rate mobile applications